> How on earth do people running Slackware manage their library dependencies and keep everything up to date?
slackpkg update
slackpkg upgrade-all
This is how you get the most recent version of all installed packages. You can run this every morning and you will have more modern tools than using ubuntu.
As for dependencies, as long as a new version does not add a new dependency, you are good. But changing dependencies of a software package is a major change that should not happen automatically. Recursive "dependency resolution" is a disgusting practice that has no place in a sane world. Dependencies are part of the API: changing dependencies is supposed to break your package, unless you do something about it.
In practice, in the rare case when this happens, you will not get any warning when upgrading. But you will get an error when running your program (that has become broken because of a missing dependency). The error message will be very clear, something like:
"Runtime error: libfoo not found"
And the solution to this problem will be evident evident:
slackpkg install libfoo